The present invention relates to aqueous based tackifier fluids and their use in stabilizing particulates in propped fractures.
Hydrocarbon-producing wells are often stimulated by hydraulic fracturing treatments. In hydraulic fracturing treatments, a viscous fracturing fluid is pumped into a producing zone at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed in the zone. Particulate solids, such as graded sand, which are often referred to as “proppant” are suspended in a portion of the fracturing fluid and then deposited in the fractures when the fracturing fluid is converted to a thin fluid to be returned to the surface. These particulates serve, inter alia, to prevent the fractures from fully closing so that conductive channels are formed through which produced hydrocarbons can flow.
To prevent the subsequent flow-back of proppant and other particulates with the produced fluids, a portion of the proppant introduced into the fractures may be coated with a curable resin that may facilitate the consolidation the proppant particles in the fracture. Typically, the resin-coated proppant is deposited in the fracture after a large quantity of uncoated proppant has been deposited therein. The partially closed fractures apply pressure to the resin-coated proppant particulates whereby the particulates are forced into contact with each other while the resin enhances the grain-to-grain contact between individual proppant particles. The action of the pressure and the resin bring about the consolidation of the proppant particles into a hard, permeable mass having compressive and tensile strength, serving to prevent unconsolidated proppant and formation sand from flowing out of the fractures with the produced fluids and damaging production equipment and/or the potential production of the well.
In conjunction with or instead of resins, some or all of the proppant may be coated with a tackifier to help control the migration of formation fines through the proppant pack. Tackifiers, by their nature, remain sticky or retain adhesive character even after being placed in the formation. Thus, as formation fines attempt to flow through the pack with formation fluids, they can become entrained with the tackifying agent so as to not be produced with produced fluids.
The use of such tackifying agents has proven particularly useful in hydrocarbon and water production, especially in coal bed methane formations. However, traditional tackifying agents require hydrocarbon-based or non-aqueous carrier fluids, which may prove problematic in certain surface terrestrial, aquatic, or marine environments. Additionally, traditional agents often fail to provide the highly elastic proppant-to-proppant bond that is desirable in certain subterranean formations. Traditional tackifying agents also often lack the ability to control the onset of “tackification” (i.e., the tackifying agent cannot be placed as a non-tacky fluid that may then be activated to become tacky). Because of this, the proppant typically should be tackified before being placed in a fracture, limiting the ability to remediate and/or tackify proppant that has already been placed. Moreover, traditional tackifying agents tend to cure over time when exposed to oxidative environments.